Why successful people fail?

Why do people successful in one organisation fail in the next ?

What makes someone successful ? the individual or the system ? Or combination?

Organisations hire people for certain skills and strengths. But many a time it's the combination of skills from multiple people and ecosystem that makes a an individual successful.

People tend to have an exaggerated sense of self importance and a lower sense of ecosystem contribution to success. This is what makes them fail or underperform in other ecosystems.

That reverse also happens. 

Somebody who underperforms in an ecosystem may perform much better in another.

It is important to understand is dynamic before making deductions on one's critical success factors.